A transmissive liquid crystal display (LCD) is one that requires a backlight to provide its illumination. Often, the backlight comprises a generally planar light-guide having a transparent side, a reflective side, and a plurality of edges. Light from one or more light sources is projected such that it enters one or more of the light-guide's edges, reflects off of the light-guide's reflective side, and is emitted through the light-guide's transparent side. The light sources may take various forms, including those of a cold-cathode fluorescent lamp (CCFL) or light emitting diode (LED) array.
In some cases, a backlight's light-guide is edge-lit by, for example, one or more CCFLs or LED arrays that are positioned adjacent one or more of the light-guide's edges. Exemplary edge-lit light-guides are disclosed in more detail in U.S. Patent Application Publication 2002/0175632 A1, entitled “LED Backlight”, and in U.S. Patent Application Publication 2004/0130884 A1, entitled “Backlight Unit of Display Device and Liquid Crystal Display Device Using the Same”.
In other cases, a backlight's light-guide is bottom-lit by, for example, one or more CCFLs or LED arrays that are positioned below the light-guide's reflective side. The light source(s) project light into a secondary light-guide positioned below the primary light-guide. Light exiting this secondary light-guide is then reflected around and into one or more edges of the primary light-guide. Exemplary bottom-lit light-guides are disclosed in more detail in U.S. Patent Application Publication 2004/0061814 A1, entitled “Backlight Device for Liquid Crystal Display and Method of Fabricating the Same”.